The disclosed invention relates in general to dot printers and more particularly to print heads capable of printing and vector plotting with a variety of line widths. Raster output is presently done with pin-printers (impact printers), thermal printers, electrostatic printers or ink jet printers. Pin-printers are noisy, slow, and susceptible to mechanical wear and breakdown. Thermal printers require special paper that is often inadequate for final copy and the dot quality is inconsistent. Electrostatic printers, besides being very expensive, usually can produce only one color. Present ink jet technology typically has low reliability, requires a pressurized ink system and has fairly low resolution (on the order of 80-100 dots per inch). With all of these technologies, the actual printing device is too cumbersome to move around or can only move slowly. These systems also typically do not enable positioning at any point on the page, but instead can print dots only at the intersections of a two-dimensional orthogonal grid of points.
Some of the problems associated with present plotters result from the pens that they use. The main quality concern in plotter output is line quality and consistency. Present felt tip plotter pens have two problems in this area. Felt tip pens are subject to wear, causing the resulting lines to get progressively thicker with use. Felt tip pens also dry out so that line quality degrades with time. Carbide tip pens have been used to overcome these problems but they require special pen force and are unreliable and difficult to use. Another potential solution to these problems are roller ball pens which are fairly new but show some promise. Ink jet pens have the advantage that the stylus never comes in contact with the paper and therefore don't wear down with use. Thus, ink jet pens are also a promising solution to these problems.
It would also be advantageous to have a single pen which can plot with a number of different line widths. Usually, different line widths are created by changing to a different width pen or by tracing repeatedly over a pattern to build up the desired thickness. The first of these methods requires the use of a multiplicity of pens and also requires interruption of a printing or plotting process to perform the exchange of pens. The second of these methods not only requires additional time to draw a pattern multiple times, but also burdens the host computer with retrace algorithms.